Multiple cable modems may send and receive information over the same physical channels in both the upstream and downstream directions in a cable plant. This creates issues related to quality of service (QoS), timing, and bandwidth allocation. A cable modem termination system (CMTS) may include one or more processes each called a media access control (MAC) domain, which manages groups of channels and their associated modems. MAC domains may be provisioned by the cable plant operator. In a typical configuration, each cable modem in a particular MAC domain receives downstream provisioning information from one downstream channel. All of these cable modems arbitrate for shared access to the same logical upstream channel(s) in the MAC domain, according to information such as MAC bandwidth allocation MAP messages provided by the CMTS. MAP information is provided continuously from the CMTS on the downstream channel.
The DOCSIS 3.0 standard has been proposed for standardizing the communication of data in cable plant communication systems. One thing that DOCSIS 3.0 specifies is the relationship of downstream and upstream channels. This information may be provisioned into a database, called the DOCSIS 3.0 simple network management protocol (SNMP) management information base (MIB). Information from this database may be applied by the CMTS to set up upstream and downstream channels to associate MAC domains and cable modems associated with each fiber node in the system. These associations of channels are known as MAC domain cable modem service groups (MD-CM-SG).
Cable modems typically range and register with the CMTS when the cable modem is booted. The CMTS assigns the cable modem logical upstream channel assignments and MAPS which indicate the timing of upstream messages for the cable modem. The provisioning tells the CMTS which groups of logical upstream channels are available for this cable modem. Cable modems may be further restricted to certain upstream/downstream channels because of their physical limitations.
FIG. 1 shows a hierarchy of the organization of MAC domains, cable modem service groups, and channels by a cable modem termination system. The cable modem termination system (CMTS) 102 may manage multiple MAC domains 104-106. Each MAC domain in turn may comprise multiple MAC domain cable modem service groups. Domain 105 comprises service groups 108-110. Each cable modem service group may comprise logical upstream channels and downstream channels that are associated with one another for the purposes of ranging, registering and providing service to a cable modem system subscribers. For example service group 109 comprises downstream channels 112-114 and physical upstream channels 116-117. Each physical upstream channel may comprise one or more logical upstream channels with different characteristics, which are shared on the physical channel in a time-division fashion. For example, physical upstream channel 117 comprises logical upstream channels 118-119.